Annealing method for high-stress single-mold preforms and its application

Abstract

The application relates to the technical field of optical fiber preparation, and particularly discloses an annealing method of a high-stress single-mode preform and application. The high-stress single-mode preform to be annealed is subjected to specific rate heating, short-time holding and gradient cooling, and the like, so that a single-mode preform with small and uniform internal stress is obtained. The single-mode preform annealed by the application can greatly reduce the single-mode rod core cracking during subsequent punching operation, ensures the polarization maintaining ability of the panda-type optical fiber obtained finally, and effectively improves the yield of the optical fiber preform. The application effectively solves the problem that, in the preparation process of the panda-type polarization maintaining optical fiber preform in the prior art, the single-mode rod has large and uneven internal stress, and the single-mode rod core cracking easily occurs during punching, and finally improves the yield of the panda-type polarization maintaining optical fiber preform.

Description

Technical Field

[0001] This invention relates to the field of optical fiber fabrication technology, and specifically discloses an annealing method and application for high-stress single-mode preforms. Background Technology

[0002] Panda-type polarization-maintaining fiber is an optical fiber fabricated using the birefringence effect. It maintains the polarization direction of transmitted light and can be used in laser processing, optical sensing, and optical communication. For panda-type polarization-maintaining fiber, the higher the birefringence effect, the better the fiber's polarization-maintaining ability. This presents new challenges for the fabrication of fiber preforms.

[0003] Currently, the boron rod insertion method is the most widely used in the fabrication of panda-type polarization-maintaining fiber preforms. This involves symmetrically drilling two holes near the core and cladding of a single-mode preform, then inserting a pre-ground boron rod into these holes to form the final fiber preform. The closer the holes and boron rods are to the core, the higher the birefringence and the better the polarization retention of the final fiber. However, due to the presence of elements with different coefficients of thermal expansion within the single-mode rod, the internal stress is uneven, increasing closer to the core. Therefore, drilling holes near the core can easily cause the core to crack, resulting in a low yield of fiber preforms. Existing technologies do not offer a specific solution to this problem. Therefore, this paper proposes an annealing method to reduce the internal stress of high-stress fiber preforms and improve the final yield, which has significant practical implications for the production and development of panda-type polarization-maintaining fibers. Summary of the Invention

[0004] To address the problem of low drilling success rates in existing panda-type polarization-maintaining fiber preforms due to high and uneven internal stress, which easily leads to core breakage during drilling, this invention provides an annealing method and application for high-stress single-mode preforms. This method utilizes a specific rate of heating, short-time holding, and gradient cooling annealing process to fully release the internal stress of the high-stress single-mode preform in a short time, effectively improving the drilling success rate.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution.

[0006] The first aspect of the present invention provides an annealing method for a high-stress single-mold preform, comprising the following steps: heating the high-stress single-mold preform to be annealed to 1090-1110°C, holding it at that temperature, then gradually cooling it to 440-460°C, and cooling it to obtain a single-mold preform to be drilled.

[0007] Preferably, the gradient cooling adopts a staged programmed cooling method, wherein in the first stage, the temperature is reduced to 940-960℃ at a cooling rate of 15-25℃ / h; in the second stage, the temperature is reduced to 740-760℃ at a cooling rate of 30-40℃ / h; and in the third stage, the temperature is reduced to 440-460℃ at a cooling rate of 60-70℃ / h.

[0008] Compared to existing technologies, this invention provides a novel annealing method for high-stress single-mode preforms. Through a process of heating, holding, and multi-gradient cooling, the quality of subsequent drilling processes is effectively improved. In practical operation, the inventors discovered that the fiber core of the single-mode preform is prone to cracking during core drilling, with the cracking occurring closer to the core, leading to a decrease in the yield of the fiber preform. After extensive investigation, the inventors found that the presence of elements with different coefficients of thermal expansion within the single-mode preform, and the high concentration of germanium in the fiber core, results in excessively high and uneven stress within the single-mode preform, with the highest stress in the core area, making it more susceptible to cracking during drilling.

[0009] Based on this, the present invention performs annealing on the single-mode preform before drilling. Through a process of heating, holding, and gradient cooling, the internal stress of the single-mode preform is balanced, releasing the high stress within the preform. The gradient cooling stage employs a gradually accelerating cooling method, effectively ensuring that the high-stress single-mode preform fully releases its internal stress within a short time at high temperatures. Furthermore, the preform is cooled naturally to 440-460℃, ensuring that no further stress is generated within the quartz preform that could affect subsequent drilling. This invention utilizes a specific annealing process to effectively solve the problem of single-mode preform core cracking during drilling due to high and uneven internal stress, thereby improving the yield of fiber preforms and the final fiber's polarization retention capability.

[0010] Preferably, the heat preservation time is 3-4 hours.

[0011] Preferably, the heating is performed using a programmed heating method, with a heating rate of 235-270℃ / h.

[0012] Preferably, the cooling is performed by natural cooling.

[0013] Preferably, the method for preparing the high-stress single-mold preform to be annealed includes the following steps:

[0014] S1. A silicon isolation layer and a core layer are sequentially deposited on the inner wall of a quartz tube using chemical vapor deposition. The rod is then shrunk to obtain a solid round rod.

[0015] S2. Thicken the solid round bar to obtain the high-stress single-mold preform to be annealed.

[0016] More preferably, in S1, the outer diameter of the quartz tube is 20-30 mm, and the wall thickness of the quartz tube is 2-4 mm.

[0017] More preferably, in S1, the thickness of the silicon isolation layer is 1-2 mm.

[0018] More preferably, in S1, the thickness of the core layer is 2-4 mm.

[0019] More preferably, in S1, the raw material used for the silicon isolation layer is silicon tetrachloride.

[0020] More preferably, in S1, the core layer is a mixture of germanium tetrachloride and silicon tetrachloride.

[0021] More preferably, in S1, the carrier gas for depositing the silicon isolation layer and the core layer is oxygen and helium in a volume ratio of 3-4:1-2.

[0022] More preferably, in S1, when depositing the silicon isolation layer, the gas flow rate of silicon tetrachloride is 100-200 sccm.

[0023] More preferably, in S1, when depositing the core layer, the gas flow rate for germanium tetrachloride is 100-200 sccm; the gas flow rate for silicon tetrachloride is 50-100 sccm.

[0024] More preferably, in S1, the temperature of the shrinking rod is 2000-2200℃.

[0025] More preferably, in S1, the number of times the shrinking rod is 6-7 times.

[0026] More preferably, in S1, the diameter of the solid round bar is 14-18 mm.

[0027] More preferably, in S2, the diameter of the high-stress single-mold preform to be annealed is 35-50 mm.

[0028] A second aspect of the present invention provides a single-mold preform to be drilled, which is prepared by the annealing method of the high-stress single-mold preform.

[0029] A third aspect of the present invention provides a panda-shaped polarization-maintaining optical fiber, which is made from the single-mode preform to be drilled.

[0030] In summary, this invention provides an annealing method and application for high-stress single-mode preforms. By subjecting the high-stress single-mode preform to annealing to specific rate heating, short-time holding, and gradient cooling, this invention obtains a single-mode preform with low and uniform internal stress. When the obtained single-mode preform is used for subsequent drilling operations, the occurrence of core cracking is significantly reduced, thereby effectively improving the yield of fiber preforms and ensuring the polarization maintenance capability of the final panda-type optical fiber. The technical solution of this invention effectively solves the problem in the prior art where the high and uneven internal stress of the single-mode preform easily leads to core cracking during drilling operations, resulting in a low yield of fiber preforms. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] This embodiment provides a high-stress single-mold preform with a diameter of 45mm, specifically including the following contents.

[0034] Step 1: A silicon isolation layer and a core layer are sequentially deposited on the inner wall of a quartz tube with an outer diameter of 28 mm and a wall thickness of 2 mm using chemical vapor deposition. During the deposition of the silicon isolation layer, the carrier gas is oxygen and helium in a volume ratio of 3.2:1.6, and the gas flow rate for loading silicon tetrachloride is 150 sccm. During the deposition of the core layer, the carrier gas is oxygen and helium in a volume ratio of 3.2:1.6, and germanium tetrachloride and silicon tetrachloride are simultaneously introduced. The gas flow rate for loading germanium tetrachloride is 150 sccm, and the gas flow rate for loading silicon tetrachloride is 75 sccm. After deposition, a quartz tube with a 1.5 mm silicon isolation layer and a 3 mm core layer on the inner wall is obtained.

[0035] Step 2: Shrink the quartz tube with a 1.5mm silicon isolation layer and a 3mm core layer on the inner wall at 2100℃. After shrinking 6 times, a solid round rod with a diameter of 16mm is obtained. Then, an outer sleeve is made on the solid round rod with a diameter of 16mm to thicken it to an outer diameter of 45mm, thus obtaining the high-stress single-mold preform to be annealed.

[0036] Step 3: Heat the high-stress single-mold preform to be annealed to 1100℃ at a heating rate of 250℃ / h, hold for 3.5h, then cool to 950℃ at a cooling rate of 20℃ / h for the first time; then cool to 750℃ at a cooling rate of 35℃ / h for the second time; and finally cool to 450℃ at a cooling rate of 65℃ / h for the third time. Cool to room temperature to obtain the single-mold preform to be drilled.

[0037] This invention drills holes in the obtained single-mode preform. After determining the drilling position based on the fact that the center positions of the two stress bars are on the same straight line as the fiber core center, two longitudinal through holes parallel to the fiber core are symmetrically drilled in the cladding area on both sides of the fiber core. The entire drilling process is smooth, with no obvious burr-like cracks inside the holes, and the single-mode rod core is intact and without cracks.

[0038] Example 2

[0039] This embodiment provides a high-stress single-mold preform with a diameter of 40mm, specifically including the following contents.

[0040] Step 1: A silicon isolation layer and a core layer are sequentially deposited on the inner wall of a quartz tube with an outer diameter of 25 mm and a wall thickness of 2 mm using chemical vapor deposition. During the deposition of the silicon isolation layer, the carrier gas is oxygen and helium in a volume ratio of 4:1.8, and the gas flow rate for loading silicon tetrachloride is 150 sccm. During the deposition of the core layer, the carrier gas is oxygen and helium in a volume ratio of 4:1.8, and germanium tetrachloride and silicon tetrachloride are simultaneously introduced. The gas flow rate for loading germanium tetrachloride is 140 sccm, and the gas flow rate for loading silicon tetrachloride is 85 sccm. After deposition, a quartz tube with a 1.5 mm silicon isolation layer and a 2.5 mm core layer on the inner wall is obtained.

[0041] Step 2: Shrink the quartz tube with a 1.5mm silicon isolation layer and a 2.5mm core layer on the inner wall at 2150℃. After shrinking 6 times, a solid round rod with a diameter of 15mm is obtained. Then, an outer sleeve is made on the solid round rod with a diameter of 15mm to thicken it to an outer diameter of 40mm, thus obtaining the high-stress single-mold preform to be annealed.

[0042] Step 3: Heat the high-stress single-mold preform to be annealed to 1090℃ at a heating rate of 240℃ / h, hold for 4h, cool down to 950℃ at a cooling rate of 20℃ / h for the first time, cool down to 750℃ at a cooling rate of 40℃ / h for the second time, and cool down to 450℃ at a cooling rate of 70℃ / h for the third time. Cool to room temperature to obtain the single-mold preform to be drilled.

[0043] This invention drills holes in the obtained single-mode preform. After determining the drilling position based on the fact that the center positions of the two stress bars are on the same straight line as the fiber core center, two longitudinal through holes parallel to the fiber core are symmetrically drilled in the cladding area on both sides of the fiber core. The entire drilling process is smooth, with no obvious burr-like cracks inside the holes, and the single-mode rod core is intact and without cracks.

[0044] Example 3

[0045] This embodiment provides a high-stress single-mold preform with a diameter of 35mm, specifically including the following contents.

[0046] Step 1: A silicon isolation layer and a core layer are sequentially deposited on the inner wall of a quartz tube with an outer diameter of 20 mm and a wall thickness of 2 mm using chemical vapor deposition. During the deposition of the silicon isolation layer, the carrier gas is oxygen and helium in a volume ratio of 3:2, and the gas flow rate for loading silicon tetrachloride is 170 sccm. During the deposition of the core layer, the carrier gas is oxygen and helium in a volume ratio of 3:2, and germanium tetrachloride and silicon tetrachloride are simultaneously introduced. The gas flow rate for loading germanium tetrachloride is 170 sccm, and the gas flow rate for loading silicon tetrachloride is 80 sccm. After deposition, a quartz tube with a 1.5 mm silicon isolation layer and a 2 mm core layer on the inner wall is obtained.

[0047] Step 2: Shrink the quartz tube with a 1.5mm silicon isolation layer and a 2mm core layer on the inner wall at 2000℃. After shrinking 7 times, a solid round rod with a diameter of 14mm is obtained. Then, an outer sleeve is made on the solid round rod with a diameter of 14mm to thicken it to an outer diameter of 35mm, thus obtaining the high-stress single-mold preform to be annealed.

[0048] Step 3: Heat the high-stress single-mold preform to be annealed to 1050℃ at a heating rate of 270℃ / h, hold for 4h, then cool to 950℃ at a cooling rate of 25℃ / h; then cool to 750℃ at a cooling rate of 40℃ / h; then cool to 450℃ at a cooling rate of 60℃ / h, and finally cool to room temperature to obtain the single-mold preform to be drilled.

[0049] This invention drills holes in the obtained single-mode preform. After determining the drilling position based on the fact that the center positions of the two stress bars are on the same straight line as the fiber core center, two longitudinal through holes parallel to the fiber core are symmetrically drilled in the cladding area on both sides of the fiber core. The entire drilling process is smooth, with no obvious burr-like cracks inside the holes, and the single-mode rod core is intact and without cracks.

[0050] Example 4

[0051] This embodiment provides a high-stress single-mold preform with a diameter of 50mm, specifically including the following contents.

[0052] Step 1: A silicon isolation layer and a core layer are sequentially deposited on the inner wall of a quartz tube with an outer diameter of 30 mm and a wall thickness of 2 mm using chemical vapor deposition. During the deposition of the silicon isolation layer, the carrier gas is oxygen and helium in a volume ratio of 3:1.6, and the gas flow rate for loading silicon tetrachloride is 150 sccm. During the deposition of the core layer, the carrier gas is oxygen and helium in a volume ratio of 3:1.6, and germanium tetrachloride and silicon tetrachloride are simultaneously introduced. The gas flow rate for loading germanium tetrachloride is 100 sccm, and the gas flow rate for loading silicon tetrachloride is 80 sccm. After deposition, a quartz tube with a 2.1 mm silicon isolation layer and a 2.7 mm core layer on the inner wall is obtained.

[0053] Step 2: Shrink the quartz tube with an inner wall of 2.1mm silicon isolation layer and a core layer of 2.7mm at 2050℃. After shrinking 7 times, a solid round bar with a diameter of 18mm is obtained. Then, an outer sleeve is made on the solid round bar with a diameter of 18mm to thicken it to an outer diameter of 50mm, thus obtaining the high-stress single-mold preform to be annealed.

[0054] Step 3: Heat the high-stress single-mold preform to be annealed to 1100℃ at a heating rate of 260℃ / h, hold for 4h, cool down to 950℃ at a cooling rate of 15℃ / h for the first time, cool down to 750℃ at a cooling rate of 18℃ / h for the second time, and cool down to 440℃ at a cooling rate of 50℃ / h for the third time. Cool to room temperature to obtain the single-mold preform to be drilled.

[0055] This invention drills holes in the obtained single-mode preform. After determining the drilling position based on the fact that the center positions of the two stress bars are on the same straight line as the fiber core center, two longitudinal through holes parallel to the fiber core are symmetrically drilled in the cladding area on both sides of the fiber core. The entire drilling process is smooth, with no obvious burr-like cracks inside the holes, and the single-mode rod core is intact and without cracks.

[0056] Example 5

[0057] This embodiment provides a high-stress single-mold preform with a diameter of 45mm, specifically including the following contents.

[0058] Step 1: A silicon isolation layer and a core layer are sequentially deposited on the inner wall of a quartz tube with an outer diameter of 28 mm and a wall thickness of 2 mm using chemical vapor deposition. During the deposition of the silicon isolation layer, the carrier gas is oxygen and helium in a volume ratio of 3.2:1.6, and the gas flow rate for loading silicon tetrachloride is 150 sccm. During the deposition of the core layer, the carrier gas is oxygen and helium in a volume ratio of 3.2:1.6, and germanium tetrachloride and silicon tetrachloride are simultaneously introduced. The gas flow rate for loading germanium tetrachloride is 150 sccm, and the gas flow rate for loading silicon tetrachloride is 75 sccm. After deposition, a quartz tube with a 1.5 mm silicon isolation layer and a 3 mm core layer on the inner wall is obtained.

[0059] Step 2: Shrink the quartz tube with an inner wall of 1.5mm silicon isolation layer and a core layer of 2.2mm at 2100℃. After shrinking 6 times, a solid round rod with a diameter of 16mm is obtained. Then, an outer sleeve is made on the solid round rod with a diameter of 16mm to thicken it to an outer diameter of 45mm, thus obtaining the high-stress single-mold preform to be annealed.

[0060] Step 3: Heat the high-stress single-mold preform to be annealed to 1100℃ at a heating rate of 200℃ / h, hold for 3.5h, then cool to 950℃ at a cooling rate of 20℃ / h for the first time; then cool to 750℃ at a cooling rate of 35℃ / h for the second time; and finally cool to 450℃ at a cooling rate of 65℃ / h for the third time. Cool to room temperature to obtain the single-mold preform to be drilled.

[0061] This invention drills holes in the obtained single-mode preform. After determining the drilling position based on the fact that the center positions of the two stress bars are on the same straight line as the fiber core center, two longitudinal through holes parallel to the fiber core are symmetrically drilled in the cladding area on both sides of the fiber core of the fiber preform. The entire drilling process is smooth, and fine burr-like cracks appear in the holes. The single-mode rod core is intact and without cracks.

[0062] Comparative Example 1

[0063] This comparative example provides a high-stress single-mold preform with a diameter of 45 mm. The difference from Example 1 is that the cooling adopts a fixed rate cooling, which is 35℃ / h, and specifically includes the following contents.

[0064] Step 1: A silicon isolation layer and a core layer are sequentially deposited on the inner wall of a quartz tube with an outer diameter of 28 mm and a wall thickness of 2 mm using chemical vapor deposition. During the deposition of the silicon isolation layer, the carrier gas is oxygen and helium in a volume ratio of 3.2:1.6, and the gas flow rate for loading silicon tetrachloride is 150 sccm. During the deposition of the core layer, the carrier gas is oxygen and helium in a volume ratio of 3.2:1.6, and germanium tetrachloride and silicon tetrachloride are simultaneously introduced. The gas flow rate for loading germanium tetrachloride is 150 sccm, and the gas flow rate for loading silicon tetrachloride is 75 sccm. After deposition, a quartz tube with a 1.5 mm silicon isolation layer and a 3 mm core layer on the inner wall is obtained.

[0065] Step 2: Shrink the quartz tube with a 1.5mm silicon isolation layer and a 3mm core layer on the inner wall at 2100℃. After shrinking 6 times, a solid round rod with a diameter of 16mm is obtained. Then, an outer sleeve is made on the solid round rod with a diameter of 16mm to thicken it to an outer diameter of 45mm, thus obtaining the high-stress single-mold preform to be annealed.

[0066] Step 3: Heat the high-stress single-mold preform to be annealed to 1100℃ at a heating rate of 250℃ / h, hold for 3.5h, cool to 450℃ at a cooling rate of 35℃ / h, and cool to room temperature to obtain the single-mold preform to be drilled.

[0067] This invention involves drilling holes in a single-mode preform. The drilling positions are determined based on the alignment of the center positions of the two stress bars with the fiber core center. Two longitudinally penetrating holes, parallel to the fiber core, are symmetrically drilled in the cladding regions on both sides of the fiber core. After drilling, cracks appear in the single-mode preform core, and obvious burr-like cracks are present inside the holes.

[0068] Comparative Example 2

[0069] This comparative example provides a high-stress single-mold preform with a diameter of 45mm. The difference from Example 1 is that the temperature is naturally cooled after being cooled to 750℃, which specifically includes the following.

[0070] Step 1: A silicon isolation layer and a core layer are sequentially deposited on the inner wall of a quartz tube with an outer diameter of 28 mm and a wall thickness of 2 mm using chemical vapor deposition. During the deposition of the silicon isolation layer, the carrier gas is oxygen and helium in a volume ratio of 3.2:1.6, and the gas flow rate for loading silicon tetrachloride is 150 sccm. During the deposition of the core layer, the carrier gas is oxygen and helium in a volume ratio of 3.2:1.6, and germanium tetrachloride and silicon tetrachloride are simultaneously introduced. The gas flow rate for loading germanium tetrachloride is 150 sccm, and the gas flow rate for loading silicon tetrachloride is 75 sccm. After deposition, a quartz tube with a 1.5 mm silicon isolation layer and a 3 mm core layer on the inner wall is obtained.

[0071] Step 2: Shrink the quartz tube with a 1.5mm silicon isolation layer and a 3mm core layer on the inner wall at 2100℃. After shrinking 6 times, a solid round rod with a diameter of 16mm is obtained. Then, an outer sleeve is made on the solid round rod with a diameter of 16mm to thicken it to an outer diameter of 45mm, thus obtaining the high-stress single-mold preform to be annealed.

[0072] Step 3: Heat the high-stress single-mold preform to be annealed to 1100℃ at a heating rate of 250℃ / h, hold for 3.5h, then cool to 950℃ at a cooling rate of 20℃ / h for the first time; then cool to 750℃ at a cooling rate of 35℃ / h for the second time; cool to room temperature to obtain the single-mold preform to be drilled.

[0073] This invention involves drilling holes in a single-mode preform. After determining the drilling positions based on the alignment of the center positions of the two stress bars with the fiber core center, two longitudinally penetrating holes, parallel to the fiber core, are symmetrically drilled in the cladding regions on both sides of the fiber core. After drilling, fine cracks appear in the single-mode preform core, and obvious burr-like cracks are present within the holes.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An annealing method of a high stress single mode preform, characterized by: The method comprises the following steps: heating a high-stress single-mode preform to be annealed to 1090-1110 DEG C, holding, and then gradiently cooling to 440-460 DEG C, and cooling to obtain a single-mode preform to be perforated; The gradiently cooling is performed by using a staged program cooling method, wherein in the first stage, the temperature is decreased to 940-960 DEG C at a rate of 15-25 DEG C / h; in the second stage, the temperature is decreased to 740-760 DEG C at a rate of 30-40 DEG C / h; and in the third stage, the temperature is decreased to 440-460 DEG C at a rate of 60-70 DEG C / h. The holding time is 3-4 h. The heating is performed by using a program heating method, and the heating rate is 235-270 DEG C / h.

2. The method of claim 1, wherein: The method for preparing the high-stress single-mode preform to be annealed comprises the following steps: S1, sequentially depositing a silicon isolation layer and a core layer on the inner wall of a quartz tube by using a chemical vapor deposition method, and shrinking the rod material to obtain a solid round rod; S2, thickening the solid round rod to obtain the high-stress single-mode preform to be annealed.

3. The method of claim 2, wherein the high stress single mode preform is annealed by: In S1, the outer diameter of the quartz tube is 20-30 mm, and the wall thickness of the quartz tube is 2-4 mm; and / or In S1, the thickness of the silicon isolation layer is 1-2 mm; and / or In S1, the thickness of the core layer is 2-4 mm.

4. The method of claim 2, wherein the high stress single mode preform is annealed by: In S1, the raw material of the silicon isolation layer is silicon tetrachloride; and / or In S1, the raw material of the core layer is a mixture of germanium tetrachloride and silicon tetrachloride.

5. The method of claim 2, wherein the high stress single mode preform is annealed by: In S1, the carrier gas for depositing the silicon isolation layer and the core layer is oxygen and helium in a volume ratio of 3-4:1-2; and / or In S1, when the silicon isolation layer is deposited, the gas flow of the silicon tetrachloride carrier is 100-200 sccm; and / or In S1, when the core layer is deposited, the gas flow of the germanium tetrachloride carrier is 100-200 sccm, and the gas flow of the silicon tetrachloride carrier is 50-100 sccm.

6. The method of claim 2, wherein the high stress single mode preform is annealed by: In S1, the temperature of the shrinking rod material is 2000-2200 DEG C; and / or In S1, the number of times of the shrinking rod material is 6-7 times; and / or In S1, the diameter of the solid round rod is 14-18 mm; and / or In S2, the diameter of the high-stress single-mode preform to be annealed is 35-50 mm.

7. A single mode preform to be drilled, characterized in that: The high-stress single-mode preform to be annealed is prepared by using the annealing method of any one of claims 1-6.

8. A panda polarisation maintaining optical fibre characterised in that: The single-mode preform to be perforated is prepared by using the method of claim 7.